(a) Field of the Invention
The present invention relates to gas turbines, and more particularly to a device for controlling the flow of cooling air through a flowpath in a turbine blade.
(b) Description of Prior Art
In a turbine engine, gases are compressed in a compressor section, burned with fuel in a combustion section and expanded in a turbine section to extract work from the hot, pressurized gases. The rotor assembly of the turbine section includes a disk having a plurality of circumferentially disposed, spaced apart blade attachment slots, each of which is provided with a turbine blade having a root radially disposed therein and spaced from the bottom part of the slot, thus leaving a cavity therebetween.
During operation of the engine, the hot gases impart energy to the rotor assembly. However, the material of the blades can tolerate a maximum temperature beyond which its vulnerability to damage increases, leading to a lower service life.
It is known to cool turbine blades by flowing cooling air extracted from the compressor section. The cooling air is flowed to the cavities formed in the rotor disk through a stator assembly supporting the combustion section and the rotor assembly. From each cavity, the cooling air is flowed through one or more flowpaths in the blade internal core from an inlet opening at the root thereof and exiting through openings provided near the trailing edge of the blade.
A problem which arises with such a configuration is that the amount of cooling air flowing through the blades cannot be adjusted for the amount of cooling air required.
Devices for adjusting the flow of cooling air into turbine blades are known. For example, U.S. Pat. No. 4,626,169 issued to Hosing et al. describes a perforated rectangular cast seal plate, which is disposed in the cavity between the slot and the blade root, against the bottom surface thereof, and which comprises baffles to accommodate a rivet to retain the blade. The seal plate is provided with a coating applied thereon by a flame spraying method and is installed by tapping it with a hammer in the cavity, the coating providing a tight fit between the seal plate and the disk walls defining the cavity.
A problem with such a device is that the casting of the seal plate needs to correspond to the exact dimensions of the cavity and cooperate with the rivet thereof, which requires expensive machining operations. The openings in the plate can also get clogged.
It would be highly desirable to be provided with an inexpensive device that could be easily inserted in the inlet opening of the blade flowpath and be retained therein.